Fluid mixing and distribution device and method for multibed reactors

ABSTRACT

A device and method are presented for the collection, mixing and distribution of fluid between reactor beds. According to various aspects, the device includes a collection tray, a mixing chamber in fluid communication with the collection tray, a rough distribution tray in fluid communication with the mixing chamber, and a distribution tray in fluid communication with the rough distribution tray. The mixing chamber includes at least one chimney positioned about mixing chamber central outlet.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.61/840,578 which was filed on Jun. 28, 2013, the contents of which arehereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

This invention relates to co-current flow reactors where a liquid flowswith a vapor through a fixed bed of catalyst. In particular, thisrelates to the internal components for controlling the flow of vapor andliquid through the reactor when there are multiple catalyst beds, andfor redistribution of the fluids.

BACKGROUND OF THE INVENTION

A wide variety of processes use co-current flow reactors, where a fluidor fluids flow over a solid bed of particulate materials, to provide forcontact between the fluid and solid particles. In a reactor, the solidmay comprise a catalytic material on which the fluid reacts to form aproduct. The fluid can be a liquid, vapor, or mixture of liquid andvapor, and the fluid reacts to form a liquid, vapor, or a mixture of aliquid and vapor. The processes cover a range of processes, includinghydrocarbon conversion, hydrocracking and hydrotreating.

Co-current reactors with fixed beds are constructed such that thereactor allows for the fluid to flow over the catalyst bed. When thefluid is a liquid, or liquid and vapor mixture, the fluid is usuallydirected to flow downward through the reactor. Multibed reactors arealso frequently used, where the reactor beds are stacked over oneanother within a reactor shell. Typically, they are stacked with somespace between the beds.

The interbed spaces are often created to provide for intermediatetreatment of the process fluid, such as cooling, heating, mixing andredistribution.

In exothermic catalytic reactions, the control of fluid temperature anddistribution is important. The temperature and composition of the fluidsfrom an upper catalyst bed and from outside of reactor should be wellmixed before being distributed to the lower catalyst bed. Initial poortemperature and composition distribution at top of a catalyst bed canpersist or grow as the process fluids move down the reactor. Hot spotscan develop and cause rapid deactivation of the catalyst and shorten thereactor cycle length. The space between catalyst beds is for theinjection of a quench gas or liquid and for fluid mixing anddistribution. In hydrocarbon processing, the quench gas is often a coolhydrogen/hydrocarbon stream. However, cooling a fluid withoutcontrolling the mixing and distribution leads to uneven reactions anduneven temperature distribution in subsequent reactor beds. And complexmixing and distribution systems takes up valuable space in a reactorchamber holding multiple catalyst beds.

Due to constraints in the height of the space between reactor beds,there is a limited amount of space for introducing a quench fluid andmixing the vapor and liquid along with the quench fluid. Particularly,for existing hydroprocessing reactors, the space between catalyst bedsis already set, and sometimes it is difficult to install new internalsfor improving mixing and distribution of fluids or for changing feed andprocess conditions within the existing interbed space without reducingthe height of catalyst beds. Even for new reactors, it is often desiredto reduce the overall height of the reactors to reduce capitalexpenditure and the profile of the reactor in a processing plant.Therefore, it is desirable to provide for good mixing and distributionof fluids between adjacent catalyst beds in a relatively short interbedspace.

The design of reactors to overcome these limitations can savesignificantly on the valuable space within a reactor for maximizingcatalyst loading. Further, it is often desirable to revamp existingreactors to improve processes with the same or reduced quench zone spacebetween catalyst beds. New reactor internals that improve theutilization of the space within a reactor shell can provide significantcost savings, and allow for revamps of existing reactors to meet newoperational and regulatory requirements.

SUMMARY OF THE INVENTION

By one aspect, a device is provided for the mixing and distribution offluid over the top of a reactor bed. The device includes collection trayhaving a top and a bottom, and having outlet ports therethrough. Amixing chamber is provided in fluid communication with the collectiontray outlet ports and has a mixing chamber outlet. A rough distributiontray is in fluid communication with the mixing chamber outlet and hasrough distribution tray liquid outlet ports therethrough. The devicealso includes at least one vapor chimney within the mixing chamberproviding fluid communication between the mixing chamber and thedistribution tray therebelow. The vapor chimney has an upper vaporchimney opening positioned within the mixing chamber and above a normaloperation liquid level of the mixing chamber.

By another aspect, a mixing device for a downflow reactor is provided.The mixing device includes a mixing chamber having an outer wall, a top,and a bottom. A generally central outlet opening extends through themixing chamber bottom. At least one inlet of the mixing chamber ispositioned radially outwardly of the central outlet opening and at leastone vapor chimney is positioned radially between the central outletopening and the inlet. The vapor chimney includes a chimney upperopening positioned within the mixing chamber above a normal operatingliquid level.

By yet another approach, a method for the distribution of fluid over thetop of a catalyst bed is provided. The method includes collecting fluidon a collection tray having a top and a bottom, and having outlet portstherethrough. The method also includes passing the liquid and vaporabove the collection tray through the outlet ports into a mixing chamberbelow the collection tray and contacting and mixing the liquid and vaporin the mixing chamber. The method further includes passing at least aportion of the liquid through a generally central outlet of the mixingchamber to a distribution tray therebelow and passing at least a portionof the vapor through a vapor chimney having an upper opening within themixing chamber radially outward of the mixing chamber outlet tointroduce the vapor portion into the distribution tray radially outwardof the liquid portion. The method further includes distributing thevapor and liquid below the distribution tray.

Other objects, advantages and applications of the present invention willbecome apparent to those skilled in the art from the following detaileddescription and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-section of a device for the collection,mixing and distribution of fluid between catalyst beds;

FIG. 2 is a schematic plan view of the arrangement of collection trayoutlet ports and vapor chimneys and central opening for mixing chamberin accordance with one approach;

FIG. 3 is a schematic plan view of the arrangement of collection trayoutlet ports and vapor chimneys and central opening for mixing chamberin accordance with another approach; and

FIG. 4 is a schematic cross-section of a device for the collection,mixing and distribution of fluid between catalyst beds in accordancewith another approach.

DETAILED DESCRIPTION OF THE INVENTION

According to various aspects, the device and apparatus disclosed hereinare disposed in the space between adjacent beds in a co-current flowvessel. For ease of explanation the following will be described in termsof a downflow reactor including two or more spaced catalyst beds, butthe mixing devices and system, and methods described herein may also beused in and applied to other hydrocarbon processing vessels havingdifferent types of processing beds. The catalyst beds in a reactor areseparated by space for quench, fluid contacting and/or mixing anddistribution of the fluids to the subsequent bed, where the mixing zonesare designed to cool/heat, mix, and sometimes condense effluent fluidsfrom a catalyst bed above. In one example, as illustrated in FIG. 1, thedevice and apparatus may be included in a hydroprocessing downflowreactor 5 and fluid flows from superior catalyst bed 30 to an inferiorcatalyst bed 32. The fluid may include vapor, liquid, or a mixture ofvapor and liquid. The reactor fluid may be quenched with a quench gas orliquid (collectively referred to as “quench fluid” herein) from a quenchfluid distributor (not shown), and the fluid is contacted, mixed andthen distributed to the inferior catalyst bed 32. It should be notedthat the term “fluid” as used herein refers to either or both of liquidand vapor. The reactor fluid and quench fluid is contacted and mixed toreduce temperature and to minimize temperature and compositiondifferences before being distributed to the inferior catalyst bed 32below the mixing zone 25. In current systems, there is considerablespace between the reactor beds for quench, mixing, and distribution. Areduction in the amount of space needed for these functions canadvantageously provide for maximum catalyst loading within the reactor 5to improve processing and performance without replacing an entirereactor. Similarly, new reactors may be designed with smaller profilesand at smaller capital expense if the height of quench zones isminimized.

Good distribution of fluid over catalyst beds is important to avoidadverse effects, such as uneven temperature rise and hot spots withinthe catalyst bed. Hot spots occurring in the catalyst beds can lead to ashortened catalyst life or to poor product quality. The methods anddevices described herein are designed to reduce the height of mixingzone 25 without sacrificing fluid mixing and distribution performance.

Turning now to FIG. 1, by one aspect a device 10 for the distribution offluid over the top of a reactor bed 32 is illustrated. The device 10 isfor collecting fluid from a first catalyst bed 30 and redistributing thefluid to a second catalyst bed 32 where the first catalyst bed 30 isabove the device 10 and the second catalyst bed 32 is below the device10. The device 10 includes a collection tray 12 and having outlet ports14, a mixing chamber 16 in fluid communication with the collection tray12, and having an outlet 18. The device further includes a roughdistribution tray 20 in fluid communication with the mixing chamberoutlet 18 and having a liquid retention weir 22 at the outer edges ofthe tray 20. The rough distribution tray may be spaced from the reactorwalls 6 to provide a generally annular opening 34 between the liquidretention weir 22 and the reactor walls 6 to facilitate the passage ofvapor from above the rough distribution tray 20 to below the roughdistribution tray 20. The rough distribution tray 20 also includes aplurality of rough distribution tray outlet ports or openings 36 toprovide for the flow of liquid therethrough. The device 10 may alsoinclude a fine distribution tray 24 positioned below the roughdistribution tray 22. The rough distribution tray 20 is in fluidcommunication with the fine distribution tray 24. The fine distributiontray 24 has a plurality of outlet ports 26 distributed over the tray 24for providing uniform distribution of fluid to the inferior catalyst bed32. The outlet ports 26 may include those generally used for finedistribution trays, including, but not limited to sieve trays, bubblecaps, and chimney distributors.

The collection tray 12 includes a plurality of outlet ports 14 fordelivering fluid to the mixing chamber, as shown in FIG. 2. The outletports 14 can be arrayed circumferentially around the tray 12, with asubstantially even spacing. In one approach, there are 4 outlet ports14. The outlet ports 14 are further designed to deliver the fluid in adirection perpendicular or oblique to the radial direction. The fluidflowing from the outlet ports 14 has a downward and circumferential flowdirection as it enters the mixing chamber. The liquid and vapor enteringthe mixing chamber 16 thus has a swirling motion thereby mixing thefluids within the chamber 16. This creates a process fluid that has amore uniform temperature and composition before redistribution of theliquid and vapor to the catalyst bed 32 below the device 10.

While various mixing chambers may be utilized in accordance with variousaspects, as are generally known in the art, in one approach, the mixingchamber 16 may include a bottom plate or tray 44 affixed to the bottomof the collection tray 12 by a sidewall or sidewalls 46. An outlet 18may be included near or at a center portion of the mixing chamber 16.The sidewalls 46 may include a single continuous sidewall that may begenerally round or have another shape. In this regard, the collectiontray bottom may form the top of the mixing chamber 16. As illustrated inFIG. 1, the sidewall includes round sidewall 46 to facilitate theswirling fluid flow in the mixing chamber 16. The outlet 18 may comprisea center opening to allow the passage of fluids therethrough, with aweir 17 surrounding the opening to retain a liquid level above thebottom tray 44 during mixing of fluids in the chamber 16.

As process fluid exits the mixing chamber 16 through the outlet 18, theliquid will pass generally downward along path 38 and collect on therough distribution tray 20 before being distributed through the outletports 36. The vapor, on the other hand, is typically intended to flowradially outwardly above the liquid along vapor flowpath 42 toward theannular opening 36 between the rough distribution tray 20 and thereactor walls 6 and to pass below the rough liquid distribution tray 20through the annular opening 34.

In previous systems, as all of the liquid and vapor passed through acenter outlet of the mixing chamber, it has been identified throughfluid dynamics studies that the vapor would predominantly flow out ofthe center of the outlet with the liquid flowing radially outside of thevapor. In this regard, in order to flow radially toward the annularopening vapor exiting the mixing chamber would have to flow radiallyacross the liquid stream. This has been found to cause high turbulenceof vapor and liquid flow. It has also been identified to result inexcessive liquid entrainment within the vapor in some circumstances asthe vapor flows through the liquid radially above the rough liquiddistribution tray. Both of these problems result in maldistribution ofliquid and vapor on the fine distribution tray and a subsequentdegradation in the distribution of fluid to the inferior catalyst bed.

By one aspect, the mixing chamber 16 includes at least one vapor chimney50 positioned within the mixing chamber for providing fluidcommunication between the mixing chamber and the rough distribution tray20 therebelow. It should be noted that while the device is describedherein as including the rough distribution tray 20 below the mixingchamber 16, other configurations are contemplated herein, such as, butnot limited to, including a splash plate below the mixing chamber 16. Inone example, shown in FIG. 1, the rough distribution tray may include asolid center portion 19 and one or more optional baffles or weirs 21surrounding the center portion 19 to slow the radial flow of liquidalong the rough distribution tray 20. In any event, a vapor chimney 50surrounds a mixing chamber vapor outlet opening 52. The vapor chimney 50includes a chimney wall 54 that extends up from the mixing chamberbottom tray 44 and includes an upper chimney inlet or opening 56 toprovide for passage of vapor into the chimney 50 and through the vaporoutlet opening 52. The upper vapor chimney opening 56 may be provided asan open top of the chimney 50 as illustrated in the figures or anaperture through the chimney wall 54. Unless specified, as used herein,upper opening refers to one or more openings that are elevated above abottom tray and/or liquid level within the mixing chamber, for examplethe mixing chamber bottom tray 44 or the liquid level within the mixingchamber. The upper vapor chimney opening 56 is preferably positioned ata height above the mixing chamber bottom tray 44 above a normaloperating liquid level to restrict liquid from entering the chimney 50and passing through the vapor outlet 52 with the vapor. In one example,the upper vapor chimney opening 56 is positioned so that at least about60% of total vapor enters vapor opening 56 and in another example, atleast about 80% of the total vapor enters vapor opening 56.

By one aspect, the vapor chimney 50 is positioned radially inwardly ofthe collection tray outlet ports 14 to facilitate contacting of liquidand vapor within the mixing chamber 16 and to restrict liquid enteringthe ports 14 from bypassing the mixing chamber 16 and falling directlythrough the vapor chimneys 50. The vapor chimney 50 is preferablypositioned radially outwardly of the mixing chamber outlet 18. In thismanner, at least a portion of the vapor within the mixing chamber 16will pass through the vapor chimneys 50 to the rough distribution tray20 therebelow rather than passing through the mixing chamber outlet 18as it flows radially inwardly through the mixing chamber 16 with aswirling motion. As a result, the vapor chimney 50 will be positionedradially outwardly of the liquid exiting the mixing chamber outlet 18 sothat it does not pass through the falling liquid. In this regard, theamount of turbulent vapor flow and liquid entrainment within the vaporalong the rough distribution tray 20 is reduced. As a result, it hasbeen found that the vertical height of the rough distribution zonebetween the rough distribution tray 20 and the mixing chamber 16 can bereduced by up to 60%, while providing similar or improved performance.Another benefit of the vapor chimney 50 is more uniform liquiddistribution through the rough distribution tray due to more uniformliquid level on the tray and less tendency of liquid being pushed to theouter edge of the tray.

As illustrated in FIG. 2, the mixing chamber outlet 18 may include agenerally central outlet opening 18 and a plurality of vapor chimneys 50may be arrayed circumferentially about the central opening 18. Thechimneys may be circumferentially spaced from each other to provide aliquid flow path therebetween.

As mentioned, the mixing chamber 16 may also include a weir 17 about thecentral outlet opening 18. The weir 17 may be provided for maintaining aminimum liquid level within the mixing chamber 16, although the normaloperating liquid level within the mixing chamber 16 may be above theheight of the weir. The upper vapor chimney opening 56 will typically bepositioned above the upper edge of the weir 17 and above the normaloperating liquid level in the mixing chamber 16. By one approach, theweir 17 is positioned radially inward of the vapor chimney 50 as shownin FIGS. 1-3. By another approach the weir 17 is positioned radiallyoutwardly of the vapor chimney 50 as shown in FIG. 4.

Turning now to FIG. 3, by one approach the plurality of vapor chimneysincludes a plurality of elongate vapor chimneys 60 positioned about themixing chamber outlet 18. The elongate vapor chimneys 60 may have alongitudinal axis 62 that is oblique to the radial direction. The vaporchimneys 60 may be spaced from one another to provide a fluid flowpaththerebetween. Preferably the longitudinal axis 62 extends generallyparallel to the direction of swirling flow of fluid 64 within thechamber 16 to reduce interference with the swirling flow of fluid. Byone approach, as shown in FIG. 3, the elongate vapor chimneys 60 mayhave a radially distal end portion 66 that is wider than a radiallyproximal end portion 68 (relative to the center opening 18) so that thewider ends partially obstruct liquid flow toward the center opening 18.This may help to maintain a normal operating liquid level within themixing chamber and also provide a minimum liquid level. In this regard,a weir as described previously may not be provided in accordance withthis aspect.

With vapor chimney 50, the mixing chamber outlet 18 is mostly for liquidflow and its diameter can be reduced significantly. The combination ofchimney area and mixing chamber outlet area is similar to the mixingchamber outlet area without chimneys, so the fluid mixing volume insidethe mixing chamber is close to the design without vapor chimneys insidethe mixing chamber.

Turning to more of the particulars, the vapor chimney 50 may extendthrough the mixing chamber bottom tray 44 or may only extend upwardlytherefrom. In this regard, the vapor chimney 50 may include a vaporchimney passageway 59 within the vapor chimney sidewalls 54 that has agenerally consistent cross section or a varying cross section.Similarly, the vapor opening 52 through the mixing chamber bottom tray44 may be similarly sized to the vapor chimney passageway 59 or mayinclude one or more smaller openings 55 arranged within the vaporchimney 50.

The device 10 can also include a quench gas injection into the spacebetween the catalyst beds 30, 32. When there is a quench gas injection,it is preferred to inject the quench gas in the vapor space above thecollection tray 12 as is generally known to those of ordinary skill inthe art. A cool quench gas may be injected at a position near the centeraxis, and sprayed in an outward radial direction or near the reactorwalls and sprayed in an inward radial direction above the collectiontray. The spray contacts the vapor and liquid flowing downward from thereactor bed above the quench zone. Heat transfer between the two gasesis generally a matter of gas mixing which depends on the momentumexchange between the two vapor streams. Heat transfer to the liquid istypically through the transfer of heat across the liquid droplet surfacearea.

While the invention has been described with what are presentlyconsidered the preferred embodiments, it is to be understood that theinvention is not limited to the disclosed embodiments, but it isintended to cover various modifications and equivalent arrangementsincluded within the scope of the appended claims.

1. A method for the mixing and distribution of fluid over the top of areactor bed, comprising: collecting fluid on a collection tray having atop and a bottom, and having outlet ports therethrough; passing theliquid and vapor above the collection tray through the outlet ports intoa mixing chamber below the collection tray and contacting and mixing theliquid and vapor in the mixing chamber; passing at least a portion ofthe liquid through a generally central outlet of the mixing chamber to adistribution tray therebelow; passing at least a portion of the vaporthrough a vapor chimney having an upper opening within the mixingchamber and positioned radially outward of the mixing chamber outlet tointroduce the vapor portion into the distribution tray radially outwardof the liquid portion; distributing the vapor and liquid below thedistribution tray.
 2. The method of claim 1, wherein the liquid andvapor are passed into the mixing chamber radially outwardly of themixing chamber vapor chimney in an inwardly swirling motion.
 3. Themethod of claim 1, wherein the portion of vapor from the vapor chimneyis passed radially outwardly along the rough distribution tray.
 4. Themethod of claim 1, further comprising passing the vapor portion througha plurality of vapor chimneys positioned radially outward of a generallycentral mixing chamber outlet.
 5. The method of claim 1, wherein theplurality of vapor chimneys are arrayed circumferentially about thegenerally central opening.
 6. The method of claim 1, further includingmaintaining a normal operating liquid level in the mixing chamber usinga weir extending about the mixing chamber outlet and passing the vaporinto the vapor chimney at a higher height above the mixing chamber floorthan the normal operating liquid level.
 7. The method of claim 1,further comprising restricting liquid from entering the mixing chambervapor chimney by positioning the upper opening above a normal operatingliquid level of the mixing chamber.
 8. The method of claim 1, furthercomprising passing the vapor portion through a plurality of elongatevapor chimneys positioned about the mixing chamber outlet.
 9. The methodof claim 8, wherein the elongate vapor chimneys include a lengthwisedimension that is oblique to the radial direction of the mixing chamberand passing liquid through fluid passageways between the elongatechimneys to reduce interference with the a swirling motion of theliquid.